1. Field of the Invention
The present invention relates to formic acid as a substantially chloride free accelerator additive for forming cementitious compositions which exhibit accelerated hardening, including superior compressive strengths, and to methods for forming such compositions. Optionally, compositions exhibiting accelerated setting as well as accelerated hardening may also be formed. The compositions and methods of this invention may be used with a wide variety of cementitious compositions including hydraulic cements such as portland cement, non-hydraulic cements such as epoxy cements, finely divided mineral admixtures such as fly ash, or any combination of these.
2. Background and Objects of the Invention
Cement compositions or cementitious materials are usually classified as hydraulic cements or non-hydraulic cements. Hydraulic cements usually require the presence of water to harden. The most significant class of hydraulic cements is portland cement. Non-hydraulic cements can harden without water, and their most important class is polymer cements. Another important class of cementitious materials is finely divided mineral admixtures, including latent hydraulic binders, or pozzolanic materials. These require the addition of a triggering material such as lime in order to form a cement. Cementitious materials may also comprise a mixed binder system, for example, a blend of a polymer and portland cement, also called polymer-modified portland cement. Concrete is formed by mixing a cement with aggregate(s), water (if required) (also called mixing water), and optionally, additive(s) also known as admixture(s). An admixture is a material other than water, aggregate(s) or cement which is used as an ingredient of concrete; it is usually added to a batch of cement or concrete immediately before or during its mixing. Admixtures may be used to alter one or more properties of concrete including acceleration, and/or improvement of strength development, water reduction and set control, air-entrainment, gas formation, color, flocculation, and reduction of alkali aggregate expansion. As an overview of the various aspects of concrete, especially hydraulic cements, see Concrete Making Materials, by S. Popovics, incorporated by reference herein. Particular reference is directed to Ch. 2 for the various types of portland cements and their properties including hardening and setting, Ch. 4 for hydraulic cements other than portland, and Ch. 6 for additives or admixtures for concretes. (See p. 134 for a listing of fifteen groups of admixtures suggested as a classification system by the American Concrete Institute.) Since many admixtures affect more than one property of concrete, sometimes adversely, the optimum use of admixtures may require careful attention to the type and amount of admixture(s) as well as the type and amount of cement or concrete used.
Control of hardening and setting is important to the construction industry. For example, accelerating the hardening of a concrete foundation may allow faster completion of a building. Those admixtures commonly called accelerators are added to increase the rate of hardening, the rate of setting or both. The most common accelerator for concrete is calcium chloride (CaCl.sub.2) either by itself or as a principal admixture ingredient. Other materials and/or mixtures have also been disclosed as accelerators.
For example, U.S. Pat. Nos. 4,264,367 and 4,264,368 to Schutz disclose a method and compositions for accelerating the setting time of portland cement using water-soluble carbonates and alpha-hydroxy carbonyl compounds.
U.S. Pat. No. 4,261,755 to Berry et al teaches the use of sodium, calcium and ammonium salts of formic acid as early strength developers and setting accelerators in hydraulic cements, concretes, mortars and plasters.
U.S. Pat. No. 3,619,211 to Kossivas discloses the use of water-soluble formate salts formed by mixing an amine with formic acid as set-accelerating additives for portland cement compositions.
U.S. Pat. No. 3,801,338 to Whitaker discloses an additive for hydraulic cement which comprises a major amount of sodium nitrite together with a minor amount of calcium formate.
U.S. Pat. No. 3,210,207 to Dodson et al teaches the use of calcium formate mixed with a member selected from the group consisting of benzoic acid and the alkali metal, alkaline earth metal, and ammonium salts of chromic, benzoic, and nitrous acid.
U.S. Pat. No. 2,880,102 to Woodard et al teaches the use of cementing compositions comprising at least one salt of the group consisting of the sodium, lithium, potassium, and ammonium salts of formic, acetic, nitrous, chloroacetic, gluconic, and tartaric acids.
While admixtures used as accelerators may increase the rate of setting or early hardening of cementitious materials they frequently do so at the expense of later strengths. Additionally, the use of admixture(s) containing chloride ion may cause corrosion problems with metallic reinforcement (usually made from steel) embedded in the concrete.
It is, therefore, an object of the present invention to provide a substantially chloride-free accelerator for use in forming cementitious compositions which exhibit improved strengths and, optionally, faster setting.
It is another object of the present invention to provide cementitious compositions and methods for their formation in which the compositions exhibit accelerated hardening, and, optionally, accelerated setting without reduction of final strength.
It is a further object to provide cementitious compositions which comprise a substantially chloride-free accelerator.
It is another object of this invention to provide finely divided mineral admixtures pretreated with formic acid wherein such material may be used to form cements exhibiting accelerated hardening including improved strength and, optionally, exhibiting accelerated setting.
It is yet a further object of this invention to provide non-hydraulic cementitious compositions including latex, acrylic, epoxy and other polymer cements, which exhibit accelerated hardening and, optionally, accelerated setting.
It is still a further object of this invention to provide cementitious compositions comprising mixed binders which exhibit accelerated hardening and, optionally, accelerated setting.
These and other objects of the invention will be apparent from the following description.